A large number of personal/home users access the Internet through cable modem networks that utilize existing cable television infrastructure to transmit/receive Internet traffic. In a typical configuration, a personal computer is connected to a cable modem that interfaces with a coaxial, hybrid fiber/coaxial cable (HFC), or optical fiber cable (fiber-optic cable) used to provide cable television service to the home. The coaxial cable is then used to transmit both Internet and television signals to the home.
More specifically, in a cable modem network, digital data is transmitted between the cable modem, typically located at the user's home or office, and a cable modem termination system (CMTS), typically located at the head end of the network. The digital data is carried using radio frequency (RF) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission to the CMTS and demodulate downstream RF signals received from the CMTS to bit streams for use by computers. Similarly, the CMTS converts downstream digital data to a modulated signal, which is carried over the fiber and coaxial lines to the user's home. On the return path, the CMTS receives the modulated upstream signals and demodulates them for transmission to an external node. One example standard for transmission of data over cable networks is the Data-Over-Cable Service Interface Specification (DOCSIS).